Method for Making Crosslinked Fluoropolymer Compositions Containing Low Level of Extractable Fluorides

ABSTRACT

A composition for manufacturing a crosslinked ethylene tetrafluoroethylene (ETFE) copolymer with enhanced abrasion resistance and heat resistance is provided, the composition including ETFE, about 0.1-10% w/w of a metal oxide that effectively scavenges high levels of fluoride ions; and a crosslinking agent. Methods of using and making the composition are also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional application under 35 U.S.C. § 120 of U.S. patentapplication Ser. No. 15/636,336, filed 28 Jun. 2017 (issued as U.S. Pat.No. 10,008,302); U.S. patent application Ser. No. 15/636,336 is acontinuing application under 35 U.S.C. § 120 of U.S. patent applicationSer. No. 14/751,345, filed on 26 Jun. 2015 (issued as U.S. Pat. No.9,728,298). The contents of the foregoing applications are incorporatedby reference herein in their entireties, although their prosecutionhistories are not incorporated herein.

BACKGROUND Field of the Disclosure

The present disclosure relates generally to polymer formulations. Suchpolymers as well as methods of their use and methods of their making areprovided.

Background

Ethylene-tetrafluoroethylene (ETFE) copolymers have a wide variety ofuseful applications. They have good structural strength, a relativelyhigh melting temperature, and excellent chemical, electrical and highenergy radiation resistance properties. ETFE has good structuraldurability and heat resistance, having a tensile strength of 6100 psi(42 N mm⁻²), with a working temperature range of −184° C. to +150° C.

ETFE is an excellent material both as the jacketing and primaryinsulator of electrical cables. Because of its properties ETFE can beused in high stress and high reliability situations. This includes, butis not limited to, aircraft and spacecraft wiring.

The resistance of ETFE to heat and abrasion can be further improved bycrosslinking the copolymer. The crosslinking is achieved in variousways. The highest levels of heat and abrasion resistance are achieved bycrosslinking by adding a crosslinking agent and irradiating the ETFEcopolymer with high-energy ionizing radiation. Unfortunately, during thecrosslinking process, hydrogen fluoride (HF) gas is released. Hydrogenfluoride is highly corrosive, and readily damages wiring and othermetallic parts. Irradiation with high-energy ionizing radiation releaseshigh concentrations of HF from the ETFE copolymer. Attempts have beenmade to subject the crosslinked ETFE coated wire cable to a heattreatment to drive the HF off the coating. However, to date theseefforts have proven ineffective. There is a long-felt need in the artfor a way to reduce the amount of residual HF in crosslinked ETFE aftercrosslinking with high-energy ionizing radiation.

SUMMARY

The following presents a simplified summary in order to provide a basicunderstanding of some aspects of the claimed subject matter. Thissummary is not an extensive overview. It is not intended to identify keyor critical elements or to delineate the scope of the claimed subjectmatter. Its sole purpose is to present some concepts in a simplifiedform as a prelude to the more detailed description that is presentedlater.

It has been unexpectedly discovered that certain metal oxides areeffective to scavenge HF, even under the demanding conditions ofradiation mediated crosslinking of ETFE.

The disclosure provides a composition for manufacturing a crosslinkedETFE copolymer with enhanced abrasion resistance and heat resistance,the composition comprising: ETFE; about 0.1-10% w/w of a metal oxideselected from the group consisting of ZnO and MgO; and a crosslinkingagent.

The disclosure further provides a method of making a crosslinked ETFEcopolymer with enhanced abrasion resistance and heat resistance, themethod comprising: providing the composition disclosed above; andexposing the composition to at least about 5 Mrad (50 kGy) ionizingradiation; wherein the level of extractable fluoride ions in thecrosslinked ETFE copolymer is less than about 150 ppm w/w. Also providedis a crosslinked ETFE copolymer that is the product of this method,having enhanced abrasion resistance, enhanced heat resistance, and alevel of extractable fluoride ions that is less than about 150 ppm w/w.

The disclosure further provides a method of making a jacket for aconducting wire with enhanced abrasion resistance and heat resistance,the method comprising: providing the composition disclosed above;extruding the composition into the shape of the jacket; and crosslinkingthe composition by exposing the composition to at least about 5 Mrad (50kGy) ionizing radiation to produce a crosslinked ETFE copolymer; whereinthe level of extractable fluoride ions in the crosslinked ETFE copolymeris less than about 150 ppm w/w. Also provided is the jacket for aconducting wire that is the product of this method, the jacket havingenhanced abrasion resistance, enhanced heat resistance, and a level ofextractable fluoride ions that is less than about 150 ppm w/w.

The disclosure further provides a method of making a primary insulatorfor a conducting wire with enhanced abrasion resistance and heatresistance, the method comprising: providing the composition disclosedabove; applying the composition to the wire; and crosslinking thecomposition by exposing the composition to at least about 5 Mrad (50kGy) ionizing radiation to produce a crosslinked ethylenetetrafluoroethylene copolymer; wherein the level of extractable fluorideions in the crosslinked ETFE copolymer is less than about 150 ppm w/w.Also provided is the primary insulator made by this method, the primaryinsulator having enhanced abrasion resistance, enhanced heat resistance,and a level of extractable fluoride ions that is less than about 150 ppmw/w.

Further provided is a concentrate for making a crosslinked ETFEcopolymer, the concentrate comprising: about 12.5-50% w/w of a metaloxide selected from the group consisting of ZnO and MgO; and ETFE.

A method of making a crosslinked ETFE is further provided, the methodcomprising providing the above concentrate; diluting the concentratewith diluent ETFE to the point at which the metal oxide concentration isabout 0.1-10% w/w, to make a diluted composition; and exposing thediluted composition to at least 5 Mrad (50 kGy) ionizing radiation;wherein the level of extractable fluoride ions in the crosslinked ETFEcopolymer is less than about 150 ppm w/w.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: A graph showing concentrations of extractable fluoride ions fromseven ETFE compositions that were not exposed to ionizing radiation (0Mrad).

FIG. 2: A graph showing concentrations of extractable fluoride ions fromseven ETFE compositions after exposure to 10 Mrad of high-energyelectron radiation.

FIG. 3: A graph showing concentrations of extractable fluoride ions fromseven ETFE compositions after exposure to 20 Mrad of high-energyelectron radiation.

DETAILED DESCRIPTION A. Definitions

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art of this disclosure. It will be furtherunderstood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the specification andshould not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein. Well known functions or constructions maynot be described in detail for brevity or clarity.

It will be understood that when a feature or element is referred to asbeing “on” another feature or element, it can be directly on the otherfeature or element or intervening features and/or elements may also bepresent. In contrast, when a feature or element is referred to as being“directly on” another feature or element, there are no interveningfeatures or elements present. It will also be understood that, when afeature or element is referred to as being “connected”, “attached” or“coupled” to another feature or element, it can be directly connected,attached or coupled to the other feature or element or interveningfeatures or elements may be present. In contrast, when a feature orelement is referred to as being “directly connected”, “directlyattached” or “directly coupled” to another feature or element, there areno intervening features or elements present. Although described or shownwith respect to one embodiment, the features and elements so describedor shown can apply to other embodiments.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a”, “an” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise.

Spatially relative terms, such as “under”, “below”, “lower”, “over”,“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another when thepropulsion unit is positioned for normal operation (i.e., right sideup).

The terms “first” and “second” are used herein to describe variousfeatures or elements, but these features or elements should not belimited by these terms. These terms are only used to distinguish onefeature or element from another feature or element. Thus, a firstfeature or element discussed below could be termed a second feature orelement, and similarly, a second feature or element discussed belowcould be termed a first feature or element without departing from theteachings of the present disclosure.

With reference to the use of the words “comprise” or “comprises” or“comprising” in the foregoing description and/or in the followingclaims, unless the context requires otherwise, those words are used onthe basis and clear understanding that they are to be interpretedinclusively, rather than exclusively, and that each of those words is tobe so interpreted in construing the foregoing description and thefollowing claims.

The term “consisting essentially of” means that, in addition to therecited elements, what is claimed may also contain other elements(steps, structures, ingredients, components, etc.) that do not adverselyaffect the operability of what is claimed for its intended purpose asstated in this disclosure. Importantly, this term excludes such otherelements that adversely affect the operability of what is claimed forits intended purpose as stated in this disclosure, even if such otherelements might enhance the operability of what is claimed for some otherpurpose.

The terms “about” or “approximately” mean within a range of reasonableerror around a central value. Such reasonable error may for example stemfrom the precision of an instrument or method used to measure the value.The error could also stem from the precision of a method of making acomponent of a device. Specific examples of such limits of reasonableerror are 20%, 10%, 5%, 2.5%, and 1%. Unless specified otherwise, allnumerical values may be approximate.

B. Composition for Manufacturing a Crosslinked ETFE Copolymer

A composition for manufacturing a crosslinked ETFE copolymer withenhanced abrasion resistance and heat resistance is provided, thecomposition comprising: ETFE; about 0.1-10% w/w of a metal oxide; and acrosslinking agent.

The ETFE is composed of monomers of ethylene (CH₂CH₂) andtetrafluoroethylene (CF₂CF₂) in various proportions. Like allcopolymers, its properties and molecular weight can be varied by varyingthe relative compositions of the ethylene and tetrafluoroethylene, as iswithin the capabilities of one of ordinary skill in the art.

The metal oxide functions to react with undesirable fluoride ions duringcrosslinking (“scavenging”). In some embodiments of the composition themetal oxide is selected from the group consisting of ZnO and MgO. Theseoxides have been discovered to have excellent fluoride ion scavengingproperties, even at the extremely high levels of fluoride ion productionthat occur during the radiologic crosslinking of ETFE copolymers.However, it has been discovered that not all metal oxides that arepresently used as fluoride ion scavengers under other conditions aresuitable for use during the radiologic crosslinking of ETFE copolymers.For example, antimony oxide (Sb₂O₃) is suitable as a fluoride ionscavenger under conditions of low or moderate fluoride ion production,but as illustrated in the below example Sb₂O₃ performs poorly as afluoride ion scavenger during the radiologic crosslinking of ETFEcopolymers; thus in some embodiments of the composition the metal oxideis not Sb₂O₃. Other oxides that scavenge fluoride ions include calciumoxide, titanium oxide, hydrotalcite (Mg₆Al₂CO₃(OH)₁₆.4(H₂O)), leadoxide, lead phosphate, and PbHPO₃.

In some embodiments of the composition the crosslinking agent istriallyl isocyanurate(1,3,5-triallyl-1,3,5-triazinane-2,4,6-trione—TAIC). TAIC is used as acrosslinking agent for rubber products and plastics products. TAIC is awaxy solid with a low vapor pressure that is not flammable. TAIC has amoderate water solubility of 3.5 g L⁻¹. TAIC is useful to catalyzecrosslinking in the presence of ionizing radiation to create anabrasion-resistant and heat-resistant crosslinked ETFE copolymer. It hasthe following structure

TAIC may be present in the composition at any concentration that iseffective to product crosslinking during exposure to ionizing radiation.In some embodiments of the composition, TAIC is present at aconcentration of about 1-10% w/w. In further embodiments, TAIC ispresent at a concentration of about 3-7% w/w. In still furtherembodiments, TAIC is present at a concentration of about 5% w/w.

The metal oxide may be present at any concentration that effectivelyscavenges HF during irradiation crosslinking. In some embodiments of thecomposition, the metal oxide is present at a concentration effective toreduce extractable HF to about 150 ppm or less during radiologic curing.In some embodiments of the composition the metal oxide is present atconcentrations of about 0.1-8% w/w. In further embodiments of thecomposition the metal oxide is present at a concentration of about atleast about 2.5% w/w. In still further embodiments, the metal oxide ispresent at a concentration of about 2.5-5.0% w/w. In a specificembodiment, the metal oxide is present at about 5% w/w.

In some cases is may be desired to add a pigment to the composition, toachieve certain coloration. The coloration may be indicative of theproperties or intended uses of a wire that is jacketed by a crosslinkedETFE copolymer. The pigment may function to protect the crosslinkedcomposition from radiation incidental to its use, for exampleultraviolet radiation that might be incidental to outdoor use. It isadvantageous if the pigment retains its pigmenting characteristics afterexposure to ionizing radiation. Some embodiments of the pigment retainits pigmenting characteristics after exposure to at least about 5 Mrad(50 kGy). Further embodiments of the pigment retain its pigmentingcharacteristics after exposure to at least about 10 Mrad (100 kGy).Still further embodiments of the pigment retain its pigmentingcharacteristics after exposure to at least about 20 Mrad (200 kGy). In aspecific embodiment the pigment is TiO₂.

C. Method of Making Crosslinked Etfe Copolymer

A method of making a crosslinked ethylene tetrafluoroethylene (ETFE)copolymer with enhanced abrasion resistance and heat resistance isprovided, the method comprising: providing any of the compositions asdescribed in the previous section; and exposing the composition to atleast about 5 Mrad (50 kGy) ionizing radiation; wherein the level ofextractable fluoride ions in the crosslinked ETFE copolymer is less thanabout 150 ppm w/w.

In the context of this disclosure, any reference to levels ofextractable fluoride ions in a crosslinked ETFE copolymer refers tolevels as measured by the following protocol. A piece of crosslinkedETFE of between 1.0-1.2 g is placed into a 60 mL polypropylene widemouth bottle. 20 mL of deionized (DI) water is introduced into the jar.Each wide mouth bottle is then tightly capped and maintained at 70° C.After 7 days (168 hours) at 70° C., the bottle is allowed to cool downto room temperature, and 20 mL of “total ionic strength adjustmentbuffer 2” (or TISAB II from Ricca Chemical Company, Arlington, Tex.) isadded to the bottle. The F⁻ ion concentration determination is carriedout using a fluoride ion selective electrode or ISE (Model DC219-F byMettler-Toledo, Columbus, Ohio). The ion selective electrode isconnected to a multi-purpose pH meter (Model Seven Multi byMettler-Toledo, Columbus, Ohio) for measurements. Manufacturerrecommended procedures were followed to calibrate the electrode usingcommercially obtained fluoride standards (Thermo-Fisher Scientific,Chelmsford, Mass.) before use.

The ionizing radiation may be any type that is effective to crosslinkETFE. In some embodiments of the method, the ionizing radiation iselectron radiation. In further embodiments, the ionizing radiation ishigh-energy electron radiation. In this context, high-energy electronradiation refers to electron radiation of above about 0.1 MeV. In aspecific embodiment of the method the high-energy electron radiation isat least 0.8 MeV. The source of the electron radiation may be, forexample, an electron beam. In an alternative embodiment, the ionizingradiation is y radiation.

The dosage of radiation used to crosslink the ETFE copolymer must besubstantial to produce the desired level of crosslinking. In someembodiments of the method the composition is exposed to about 5-25 Mrad(50-250 kGy) of the ionizing radiation. In further embodiments thecomposition is exposed to about 10-20 Mrad (100-200 kGy) of the ionizingradiation. In specific embodiments, the composition is exposed to about10 or about 20 Mrad (100 or 200 kGy) of the ionizing radiation.

The level of extractable fluoride in the crosslinked ETFE copolymer(measured as described above) will ideally be sufficiently low toprevent damage to nearby structures, such as a metal wire. In someembodiments of the method, the level of extractable fluoride ions in thecrosslinked ETFE copolymer is less than about 80 ppm w/w. In furtherembodiments of the method, the level of extractable fluoride ions in thecrosslinked ETFE copolymer is less than about 60 ppm w/w. In yet furtherembodiments of the method, the level of extractable fluoride ions in thecrosslinked ETFE copolymer is less than about 20 ppm w/w. In stillfurther embodiments of the method, the level of extractable fluorideions in the crosslinked ETFE copolymer is less than about 10 ppm w/w. Ina specific embodiment of the method, the level of extractable fluorideions in the crosslinked ETFE copolymer is less than about 5 ppm w/w.

A crosslinked ETFE copolymer with enhanced abrasion resistance and heatresistance that is the product of any of the above processes is alsoprovided, in which the crosslinked ETFE copolymer has a level ofextractable fluoride ions as also described above.

D. Methods of Making Jackets and Primary Insulators

The crosslinked ETFE copolymers disclosed above are of particularutility as jacketing and primary insulation for electrically conductingwire. The low levels of extractable fluoride ions prevent corrosion ofthe metal wire, while still allowing high levels of crosslinking causedby high-intensity ionizing radiation.

A method of making a jacket for a conducting wire with enhanced abrasionresistance and heat resistance is provided, the method comprising:providing any of the compositions for manufacturing crosslinked ETFEcopolymers provided above; extruding the composition into the shape ofthe jacket; and crosslinking the composition by exposing the compositionto at least about 5 Mrad (50 kGy) ionizing radiation to produce acrosslinked ETFE copolymer; wherein the level of extractable fluorideions in the crosslinked ETFE copolymer is less than about 150 ppm w/w.The method of extrusion may be any that is known to be suitable in theart for making such jacketing.

A method of making a primary insulator for a conducting wire withenhanced abrasion resistance and heat resistance is provided, the methodcomprising: providing any of the compositions for manufacturing thecrosslinked ETFE provided herein; applying the composition to the wire;and crosslinking the composition by exposing the composition to at leastabout 5 Mrad (50 kGy) ionizing radiation to produce a crosslinked ETFEcopolymer; wherein the level of extractable fluoride ions in thecrosslinked ETFE copolymer is less than about 150 ppm w/w

In each of the methods provided in this section, the radiation may be ofany type or dose that is disclosed above as suitable for the method ofmaking the crosslinked ETFE copolymer. In addition, the levels ofextractable fluoride ions may be any that is disclosed above as suitablefor the method of making the crosslinked ETFE copolymer.

A jacket for a conducting wire that is the product of any of the methodsin this section is provided, the jacket having enhanced abrasionresistance, enhanced heat resistance, and a level of extractablefluoride ions that is less than about 150 ppm w/w. A primary insulatorfor a conducting wire that is the product of any of the methods in thissection is provided, the primary insulator having enhanced abrasionresistance, enhanced heat resistance, and a level of extractablefluoride ions that is less than about 150 ppm w/w.

E. Concentrate for Making a Crosslinked ETFE Copolymer

The compositions provided in this disclosure may be prepared from aconcentrated “masterbatch.” A general embodiment of the concentratecomprises an ETFE carrier resin and a metal oxide fluoride ion scavengerat a concentration of at least 10% w/w. In some embodiments, the metaloxide concentration is about 12.5-50% w/w. In further embodiments themetal oxide concentration is about 50% w/w. The metal oxide may be anythat is disclosed as being suitable for the composition above.

The concentrate is used by diluting it down in ETFE diluent until themetal oxide is within the desired range. A method of making acrosslinked ETFE is provided, the method comprising: providing theconcentrate above; diluting the concentrate with diluent ETFE to thepoint at which the metal oxide concentration is about 0.1-10% w/w, tomake a diluted composition; and exposing the diluted composition to atleast 5 Mrad (50 kGy) ionizing radiation; wherein the level ofextractable fluoride ions in the crosslinked ETFE copolymer is less thanabout 150 ppm w/w. In some embodiments of the method, the concentrate isdiluted to the point at which the metal oxide concentration is about0.1-8% w/w. In further embodiments of the method, the concentrate isdiluted to the point at which the metal oxide concentration is at leastabout 2.5% w/w. In still further embodiments of the method, theconcentrate is diluted to the point at which the metal oxideconcentration is about 2.5-5.0% w/w. In a specific embodiment of themethod, the concentrate is diluted to the point at which the metal oxideconcentration is about 5% w/w.

In some embodiments of the method the ETFE diluent comprises acrosslinking agent. The crosslinking agent may be any of thecrosslinking agents disclosed above as suitable in the composition, suchas TAIC. In other embodiments of the method the crosslinking agent maybe added to the diluted composition. In any such embodiments, the TAICmay be present in the diluted composition at a concentration of about1-10% w/w. In further embodiments, the TAIC may be present in thediluted composition at a concentration of about 3-7% w/w. In stillfurther embodiments the TAIC may be present in the diluted compositionat a concentration of about 5% w/w.

F. Working Example

Seven ETFE compositions were prepared to test the ability of three metaloxides to scavenge fluoride ions during radiologic crosslinking of theETFE. All of the compositions contained 5% w/w of TAIC as a crosslinkingagent. A control was prepared without metal oxide. Three metal oxideswere tested: antimony trioxide (Sb₂O₃), zinc oxide (ZnO), and magnesiumoxide (MgO). Two sets of duplicate test samples were prepared for eachoxide, one set at 2.5% w/w oxide and another set at 5% w/w oxide. Thecompositions of each sample are summarized in the table below:

TABLE 1 Compositions of Test Samples Sample ETFE TAIC Sb₂O₃ ZnO MgOReference (w/w) (w/w) (w/w) (% w/w) (% w/w) A 95% 5% 0% 0% 0% B 92.5%  5% 2.5%   0% 0% C 90% 5% 5% 0% 0% D 92.5%   5% 0% 2.5%   0% E 90% 5% 0%5% 0% F 92.5%   5% 0% 0% 2.5%   G 90% 5% 0% 0% 5%The ETFE compositions listed in Table 1 were prepared at ColorantChromatics (Bethel, CT). The samples in pellet form were thencompression molded at PBY Plastics (Ontario, CA) into sheets with adimension of about 6″ (15.24 cm) by 6″ (15.24 cm) by 1/16″ (1.59 mm).These samples in sheet form were then sent to E-BEAM, Inc. (Lebanon,Ohio) for electron beam exposure experiments. For each ETFE composition,two levels of electron beam exposure dosages were used: 10 Mrad and 20Mrad. After electron beam exposure, a die cutter was used to cut out twosmall pieces from each composition to perform the extraction test.

Each piece was weighed before being placed into a 60 mL polypropylenewide-mouth bottle. The weight of each cut piece was approximately1.0-1.2 g. 20 mL of deionized water was introduced into each wide-mouthbottle using a pipette. Each wide mouth bottle was tightly capped thenplaced inside an oven at 70° C. for 7 days (168 hours). After thesamples cooled down to room temperature, 20 mL of “total ionic strengthadjustment buffer 2” (or TISAB II from Ricca Chemical Company,Arlington, Tex.) was added into each bottle. The fluoride ionconcentration determination was carried out using a fluoride ionselective electrode or ISE (Model DC219-F by Mettler-Toledo, Columbus,Ohio).

The ion selective electrode was connected to a multi-purpose pH meter(Model Seven Multi made by Mettler-Toledo, Columbus, Ohio) formeasurements. The manufacturer's recommended procedure was followed tocalibrate the electrode using commercially obtained fluoride standards(Thermo-Fisher Scientific, Chelmsford, Mass.). After the fluorideconcentration was determined for each composition (replica of two), theaverage value for each composition was calculated. The value determinedby this method is expressed in terms of μg mL⁻¹. Due to variations insample weight, the data were converted into units of μg fluoride (g ofsample)⁻¹ for comparison. As can be seen from the results shown in Table2 below, addition of 2.5% w/w of either ZnO (sample D) or MgO (sample F)dramatically reduced the extractable fluoride ion contents by as much as99%. Note that antimony trioxide, while having some ability to scavengefluoride ions under these conditions, did not provide the same dramaticlevels of reduction provided by ZnO and MgO.

TABLE 2 Extractable Fluoride After Radiologic Crosslinking 0 Mrad MetalConcentration (ppm F, 10 Mrad 20 Mrad Oxide (w/w) (ppm F, w/w) w/w) (ppmF, w/w) Sb₂O₃ 2.5% 4.6 187.2 257.2 Sb₂O₃   5% 5.0 171.3 236.6 ZnO 2.5%2.2 8.1 11.9 ZnO   5% 2.1 7.0 8.8 MgO 2.5% 2.9 4.1 8.3 MgO   5% 2.6 4.57.1 Control 3.4 743.8 1228.6At 10 Mrad, the samples containing MgO have extractable fluoride ionsthat are only marginally above baseline (0 Mrad).

As can be seen in FIG. 1, in the absence of irradiation none of thesamples contained more than 5 ppm w/w extractable fluoride. Turning nowto FIG. 2 (note the log scale), it can be seen that after irradiation at10 Mrad magnesium oxide at both concentrations reduced the amount ofextractable fluoride ions by over 99.4%. Zinc oxide at 2.5% w/w and 5%w/w reduced extractable fluoride ions by 98.9% and 99.1%, respectively.In contrast, antimony trioxide at 2.5 and 5% w/w reduced extractablefluoride ions by a lesser extent (74.8% and 77.0%, respectively).

As can be seen in FIG. 3, when the dosage of ionizing radiation wasincreased to 20 Mrad, the magnesium oxide at both concentrationsscavenged a comparable fraction of the fluoride ions as it did at 10Mrad (about 99.3 and 99.4% w/w respectively at 2.5 and 5% w/w). Thescavenging efficiency of ZnO slightly increased when the dosage ofionizing radiation was increased to 20 Mrad; at 20 Mrad the scavengingefficiency of ZnO was 99.0% at 2.5% w/w and 99.3% at 5% w/w. At 20 Mradantimony trioxide showed markedly lower scavenging efficiencies thaneither of ZnO or MgO, having scavenging efficiencies of 79.1% at 2.5%w/w and 80.7% at 5% w/w.

Moreover, at both radiation doses antimony trioxide was unable tomaintain extractable fluoride at a level that is practical for using theETFE copolymer with metallic structures such as wire, which aregenerally considered to be below about 80 ppm w/w.

G. Conclusions

It is to be understood that any given elements of the disclosedembodiments of the invention may be embodied in a single structure, asingle step, a single substance, or the like. Similarly, a given elementof the disclosed embodiment may be embodied in multiple structures,steps, substances, or the like.

The foregoing description illustrates and describes the processes,machines, manufactures, compositions of matter, and other teachings ofthe present disclosure. Additionally, the disclosure shows and describesonly certain embodiments of the processes, machines, manufactures,compositions of matter, and other teachings disclosed, but, as mentionedabove, it is to be understood that the teachings of the presentdisclosure are capable of use in various other combinations,modifications, and environments and are capable of changes ormodifications within the scope of the teachings as expressed herein,commensurate with the skill and/or knowledge of a person having ordinaryskill in the relevant art. The embodiments described hereinabove arefurther intended to explain certain best modes known of practicing theprocesses, machines, manufactures, compositions of matter, and otherteachings of the present disclosure and to enable others skilled in theart to utilize the teachings of the present disclosure in such, orother, embodiments and with the various modifications required by theparticular applications or uses. Accordingly, the processes, machines,manufactures, compositions of matter, and other teachings of the presentdisclosure are not intended to limit the exact embodiments and examplesdisclosed herein. Any section headings herein are provided only forconsistency with the suggestions of 37 C.F.R. § 1.77 or otherwise toprovide organizational queues. These headings shall not limit orcharacterize the invention(s) set forth herein.

I claim:
 1. A method of making a crosslinked ethylenetetrafluoroethylene (ETFE) copolymer with enhanced abrasion resistanceand heat resistance, the method comprising: (a) providing a compositioncomprising: (i) a fluoropolymer fraction consisting essentially of ETFE;(ii) a metal oxide selected from the group consisting of ZnO and MgO;and (iii) at least 1% w/w triallyl isocyanurate (TAIC) as a crosslinkingagent; and (b) exposing the composition to at least about 5 Mrad (50kGy) ionizing radiation; wherein the level of extractable fluoride ionsin the crosslinked ETFE copolymer is less than about 150 ppm w/w.
 2. Themethod of claim 1, in which the TAIC is present at a concentration of upto about 10% w/w.
 3. The method of claim 1, in which the TAIC is presentat a concentration of about 3-7% w/w.
 4. The method of claim 1, in whichthe TAIC is present at a concentration of about 5% w/w.
 5. The method ofclaim 1, in which the metal oxide is present at a concentration of about0.1-8% w/w.
 6. The method of claim 1, in which the metal oxide ispresent at a concentration of at least about 2.5% w/w.
 7. The method ofclaim 1, in which the metal oxide is present at a concentration of about2.5-5.0% w/w.
 8. The method of claim 1, in which the metal oxide is MgOpresent at a concentration of about 2.5-5.0% w/w.
 9. The method of claim1, in which the metal oxide is ZnO present at a concentration of about2.5-5.0% w/w.
 10. The method of claim 1, in which the ionizing radiationis electron radiation.
 11. The method of claim 1, in which the ionizingradiation is high-energy electron radiation.
 12. The method of claim 1,in which the ionizing radiation is high-energy electron radiation of atleast about 0.1 MeV.
 13. The method of claim 1, in which the ionizingradiation is high-energy electron radiation of at least about 0.8 MeV.14. The method of claim 1, in which the ionizing radiation ishigh-energy electron radiation in the form on an electron beam.
 15. Themethod of claim 1, in which the composition consists essentially of: (a)the ethylene tetrafluoroethylene; (b) the metal oxide; and (c) the TAIC.16. The method of claim 1, in which the fluoropolymer fraction consistsof the ethylene tetrafluoroethylene.
 17. The method of claim 1, in whichthe composition consists of: (a) the ethylene tetrafluoroethylene; (b)the metal oxide; and (c) the TAIC.
 18. The method of claim 1, in whichthe composition is exposed to about 5-25 Mrad (50-250 kGy) of theionizing radiation.
 19. The method of claim 1, in which the compositionis exposed to about 10-20 Mrad (100-200 kGy) of the ionizing radiation.20. The method of claim 1, in which the composition is exposed to about20 Mrad (200 kGy) of the ionizing radiation.
 21. The method of claim 1,in which the composition further comprises a pigment that retains itspigmenting characteristics after exposure to at least about 5 Mrad (50kGy).
 22. The method of claim 1, in which the composition furthercomprises a TiO₂ pigment.
 23. A crosslinked ETFE copolymer that is theproduct of the method comprising: (a) providing a compositioncomprising: (i) a fluoropolymer fraction consisting essentially of ETFE;(ii) a metal oxide selected from the group consisting of ZnO and MgO;and (iii) at least 1% w/w triallyl isocyanurate (TAIC) as a crosslinkingagent; and (b) exposing the composition to at least about 5 Mrad (50kGy) ionizing radiation; the copolymer having enhanced abrasionresistance, enhanced heat resistance, and a level of extractablefluoride ions that is less than about 150 ppm w/w.